Spring seal

ABSTRACT

A sealing ring firmly grips a movable piston, performs the normal sealing function, and when pressure is released on the piston the sealing ring pulls back on the piston so as to retract the piston. The sealing ring is designed so as to fit in a conventional seal or &#34;O&#34; ring groove without any modification of the groove.

This is a division of application Ser. No. 53,883, filed July 2, 1979and now U.S. Pat. No. 4,229,013.

BACKGROUND

In devices such as disk brakes, a lining is moved into contact with thebrake disk by way of a piston. It is conventional to provide a springfor returning the piston to its original position. Under a number ofcircumstances, the springs do not perform their intended functionwhereby the linings frictionally contact the brake disk even when nopressure is applied to the pistons.

The present invention solves that problem by providing a sealing ringwhich retracts the piston for a predetermined distance which issufficient to prevent the linings from remaining in contact with thebrake disk. For relevant prior art, see U.S. Pat. No. 4,058,084 whereinthe groove for the sealing ring is non-conventional and/or a spring isprovided in the groove with the sealing ring. The sealing ring of thepresent invention is designed to be used in a standard groove with thesealing ring performing the added function of acting like a returnspring. Also see U.S. Pat. No. 3,771,801 wherein the seal disclosedtherein bears a superficial resemblance to the seal of the presentinvention.

SUMMARY OF THE INVENTION

In accordance with the present invention, a seal assembly is providedand comprises an annular sealing ring of resilient deformable plasticmaterial and a mating back-up ring. The sealing ring has a radiallydisposed side face which defines the pressure side of the assembly. Thesealing ring has an inner peripheral surface defined by three discreteportions. The first portion converges toward said side face with a taperat an angle of between 3° and 10° with respect to the axis of thesealing ring. The second portion is contiguous with the first portionand is an angled surface between 20° and 40° with respect to a radius ofthe sealing ring. The third portion is contiguous to the second portionand is an axially extending flange adjacent the outer periphery of thesealing ring. The back-up ring is disposed radially inwardly of thethird portion and has radially disposed side faces.

It is an object of the present invention to provide a novel sealassembly wherein a sealing ring performs a dual function of acting as aseal and acting as a return spring.

It is another object of the present invention to provide a novel sealassembly for use in a stationary portion of a device and capable ofretracting a piston for a short distance when pressure on the piston isreleased, with the assembly being adapted for use in a conventional sealgroove.

It is another object of the present invention to provide a seal assemblywhich solves a problem in connection with dragging brakes in a mannerwhich is simple, inexpensive and reliable.

Other objects will appear hereinafter.

For the purpose of illustrating the invention, there is shown in thedrawings a form which is presently preferred; it being understood,however, that this invention is not limited to the precise arrangementsand instrumentalities shown.

FIG. 1 is a sectional view through a typical brake assembly in which thepresent invention may be incorporated.

FIG. 2 is an enlarged detail view showing the seal assembly in sectionand mounted in a groove before contact between the seal assembly andpiston.

FIG. 3 is a view similar to FIG. 1 but shows the orientation ofcomponents when the inner peripheral surface of the sealing ringcontacts the outer peripheral surface of a piston.

FIG. 4 is a view similar to FIG. 3 showing the orientation of thecomponents when full pressure has been applied to the piston.

FIG. 5 is a graph showing spring back travel in inches versus pressureapplied to the piston for a given size brake piston.

Referring to the drawings in detail, wherein like numerals indicate likeelements, there is shown in FIG. 1 a disk brake representing a typicalenvironment in which the seal assembly of the present invention may beincorporated. The brake 10 is conventional and per se forms no part ofthe present invention.

The brake 10 includes a housing 12 having a disk 14 between a pair oflinings 16 and 18. Lining 16 abuts piston 20. Lining 18 abuts piston 22.Each piston may have a retraction spring coaxial therewith forretracting the pistons and their associated linings in the absence ofpressure but such springs are unnecessary.

Fluid pressure may be applied to the lefthand end of piston 20 and therighthand end of piston 22 by way of fluid passage 24 in the housing 12.A seal assembly 26 is provided in a stationary portion of the housing 12for sealing contact with the outer periphery of piston 20. A similarseal assembly is provided for piston 22. The seal assemblies 26 and 28are identical. Hence, only seal assembly 28 will be described in detail.

Referring to FIG. 2, the housing 12 is provided with a standard seal orgland 30. Within the groove 30, there is provided the seal assembly 28of the present invention. The seal assembly 28 includes a sealing ring32 and a back-up ring 34. Ring 32 has a radially disposed side face 36on the pressure side. That is, surface 36 is the surface exposed to thepressure applied to the piston 22. The inner periphery of the sealingring 32 is defined by three contiguous surfaces, namely surfaces 38, 40and 42. Surface 38 converges toward the surface 36 at an angle ofbetween 3° and 10° with respect to the axis of sealing ring 32. Thepreferred taper is 4° to 6°. We have found that a taper of less than 4°for surface 38 is undesirable since there is insufficient gripping ofthe piston by the sealing ring. We have found that a taper in excess of10° is undesirable since the sealing ring is virtually locked to thepiston.

The intersection of surfaces 38 and 40 is rounded as shown in FIG. 2.Surface 40 extends at an angle of between 20° and 40° with respect to aradius of the sealing ring 32. The preferred angle for surface 40 isbetween 28° and 32° with respect to a radius on the sealing ring 32. Thesurface 42 defines the inner periphery of an axially extending flange 43on the sealing ring 32. The axial thickness of the seal assembly 28 isless than the width of the groove 30 thereby leaving a space 44 on thepressure side of the groove 30. The bottom corners of the groove 30 maybe rounded if desired with a slight mismatch on a rounded corner offlange 43 to thereby leave a crescent shaped space 46.

The back-up ring 34 has radially disposed side faces 48 and 50. Assembly28 has a triangular space 52 on its inner periphery and defined by thesurface 40 and face 50. The outer peripheral corner of ring 34contiguous with space 52 is defined by a curved surface 54. Theintersection of surfaces 42 and 40 is defined by a curved surface 56.The radius of curvature for surfaces 54 and 56 is identical but thecenter points are offset thereby resulting in space 52 at its outerperiphery having a curved tail between surfaces 54 and 56.

The inner diameter of sealing ring 32 is smaller than the outer diameterof the associated piston such as piston 22. When piston 22 is moved soas to be coaxial with and surrounded by the sealing ring 32, the sealingring 32 deforms to the shape as illustrated in FIG. 3. In FIG. 3, itwill be noted that the sealing ring 32 has been deformed so as to bulgesurface 36 outwardly into the space 44. Also, surface 40 has beendeformed so as to make the space 52 smaller but still of the samegeneral shape. The preferred squeeze level range is 11 to 21%.

When pressure is applied to the piston 22, and it moves from right toleft in FIGS. 3 and 4, the sealing ring 32 deforms to the shape shown inFIG. 4. Spaces 52 and 46 have disappeared while space 44 issubstantially larger. When the pressure is released, sealing ring 32assumes the shape as shown in FIG. 3 and retracts the piston 22 fromleft to right. The amount of retraction of piston 22 by the sealing ring32 is a function of fluid pressure applied to the piston. As shown inFIG. 5, the sealing ring 32 retracts the piston 22 between 0.010 inchwhen the pressure is 50 pounds per square inch and 0.022 inch when thepressure is 400 pounds per square inch. Surprisingly, increasing thepressure up to 600 pounds per square inch or higher had no effect on theamount of retraction of the piston by the sealing ring 32. The abovefigures represent mesured results for a specific seal size of a 0.220cross-section (nominal 3/16 inch cross-section).

The preferred material for sealing 32 is a rubber material from theethylene-propylene family for compatability with automotive brakefluids. Other resilient rubbers can be used as dictated by fluid choiceor extreme temperature conditions. Of importance is the selection of ahighly resilient rubber compound with minimal compression setcharacteristics. The back-up ring 34 is preferably made from a materialsold commercially as NYLATRON which is injection molded or machined intothe shape shown. The back-up ring 34 can be made of other conventionalback-up materials such as TFE nylon, phenolic, metal, as thecircumstance may dictate.

The space 44 should be sufficient to allow thermal expansion of the sealassembly at the maximum operating temperatures. In order to facilitateease of assembly and to facilitate distortion of the sealing ring 32, weprefer that the space 44 have a width of 5 to 15% of the seal grooveaxial length.

In a preferred embodiment of the sealing ring 32, the ring had an outernominal diameter of 3.143 inches with the radial length of surface 36 inFIG. 2 being a nominal length of 0.215 inch. When sealing ring 32 isdistorted radially outwardly by the piston 22 as shown in FIG. 3,surface 36 along a radius was decreased by approximately 0.025 to 0.030inch. Thus, the length of surface 36 along a radius decreased betweenabout 8 to 14% due to deformation by the piston 22 when comparing FIGS.2 and 3. We have found that a ring constructed in this manner willrepetitively pull the piston back a sufficient amount so as to preventthe linings 16, 18 from contacting the disk 14 when pressure isreleased. A separate spring is not required and the groove 30 is astandard seal groove requiring no special machining or shape. The curvedsurfaces 54, 56 prevent the concentration of stress when the sealingring 32 assumes the position shown in FIG. 4.

The back-up ring 34 must have an inner diameter which is equal to orgreater than the maximum outer diameter of the piston associatedtherewith. The axial thickness of the back-up ring 34 with respect tothe axial length of the groove 30 may between 15 and 25%. The sealassembly of the present invention may be a male or female so long as thegroove containing the same is stationary.

The present invention may be embodied in other specific forms withoutdeparting from the spirit or essential attributes thereof and,accordingly, reference should be made to the appended claims, ratherthan to the foregoing specification, as indicating the scope of theinvention.

We claim:
 1. A method comprising the steps of providing an annual sealassembly including a sealing ring and a back-up ring with the assemblyhaving a generally trianular opening between said rings on its innerperiphery, placing said assembly in a stationary rectangular groovehaving an axial length greater than the axial length of the assembly soas to provide a space on the high pressure side of the groove, deformingthe sealing ring radially outwardly by contact between the outerperiphery of a piston and a surface on the sealing which tapers from thehigh pressure side to said triangular opening, decreasing the size ofsaid opening by said deforming step, using a piston whose outer diameteris greater than the inner diameter of the sealing ring tapered surfacein the relaxed state of the sealing ring, applying pressure to thepiston and to said space so that said sealing ring deforms axially intoand occupies said triangular opening and biases said back-up ringradially inwardly, releasing pressure on said piston and seal assembly,and using said sealing ring as a return spring for retracting the pistona predetermined amount as said sealing ring returns to its originalcross-sectional shape as deformed by the outer periphery of said piston.2. A method in accordance with claim 1 including using a back-up ringwhich has a radially disposed side face defining one side of saidgenerally triangular opening, spacing the outermost surface of saidback-up ring from the bottom of the groove by a portion of said sealingring.
 3. A method in accordance with claim 1 including retracting thepiston by said sealing ring for a distance between about 0.010 and 0.022inch.